The temperature of the working medium of a gas turbo set may change relatively quickly as a function of the current operating state. In particular, during the startup and shutdown and in the event of load changes, the components through which the working medium flows are heated or cooled to a great extent, whereas the other components experience a substantially slower temperature change.
Gas turbo sets are known with inner shells serving for routing the working medium and an outer housing for supporting and centering the inner shells. Such housings and inner shells possess a relatively low mass. They are therefore heated relatively quickly and can cool again quickly. By contrast, both the heating and the cooling of the rotors of the compressor and turbine last substantially longer because of their high mass. In view of the resulting different thermal expansion of the components mentioned, the blade play must be such that a brushing of the moving blades against the inner shells or the guide vanes against the rotor shaft is avoided under all operating conditions. The greatest play is required in the event of what is known as a hot start. In order to ensure this blade play, a greater play than that which is necessary per se must be allowed for under full load. However, this reduces the efficiency of the gas turbo set.
In the known gas turbo sets equipped with an outer housing, the latter assumes both the carrying function for the inner shell and the pressure load occurring due to the working medium. On account of this double function, the outer housing cannot be adapted optimally to one of the two tasks, because cutbacks in this case would be necessary in the other respective function.
In particular, during each vane change, the gas turbo set has to be opened in the mid-plane, this being highly labor-intensive. Moreover, the exchange of the vanes can be commenced only when the plant has cooled sufficiently. This results in long standstill times, along with a corresponding interruption in the power output of the gas turbo set.
So that the gas turbo set can be mounted and demounted more simply and more quickly, in other solutions the outer housing has a multipart design. In these solutions, the various housing parts are connected to one another both in the axial direction and in the parting plane by means of flanges. However, such a design is complicated and therefore costly.
A gas turbo set, such as reproduced in FIGS. 1 to 3, was proposed in DE 195 44 011.
The gas turbo set 29 shown in FIGS. 1 to 3 consists of a compressor 1, a turbine 2 and a combustion chamber 3 arranged between these. The compressor 1 and the turbine 2 are arranged on a common rotor shaft 4 which carries a plurality of rows of compressor moving blades 5 and turbine moving blades 6 (FIG. 1).
The gas turbo set 29 possesses a common outer housing 7 in the form of a carrying structure, consisting of two cruciform bearing supports 9 arranged vertically to the flow direction 8 of the working medium and of two or more longitudinal members 10 oriented at right angles to these and connecting the cruciform bearing supports 9 to one another. Each cruciform bearing support 9 is formed by two concentric rings 11, 12. To connect the rings 11, 12, radial ribs 13 are arranged between them. The longitudinal members 10 are distributed uniformly on the circumference of the outer ring 12 and are connected to the latter in a suitable way releasably or unreleasably, for example by means of a welded joint (FIG. 2).
A plurality of vane carriers 14 designed as annular carrying disks are arranged at right angles to the axis of the rotor shaft 4 in the space between the cruciform bearing supports 9 and the longitudinal members 10 and are connected positively to the longitudinal members 10. For this purpose, the carrying disks 14 have corresponding recesses 15 (FIG. 2) which correspond to the shape of the longitudinal members 10. The carrying disks 14 are thus fastened axially displaceably to the longitudinal members 10. In order to fix the axial position of the carrying disks 14, the latter may be additionally screwed (not illustrated) to the longitudinal members 10. A nonpositive or materially integral connection or a combination of types of connection known per se is, of course, likewise possible. A corresponding number of compressor guide vanes 17 and turbine guide vanes 18 (FIGS. 1, 3) is fastened to the carrying disks 14 by means of vane bases 16.
In the downstream region of the compressor 1 and on the turbine side are arranged, inside the cruciform bearing supports 9, the longitudinal members 10 and the carrying disks 14, cooling ducts 19 or other suitable means which are connected to the compressor 1 and which can be acted upon by a liquid or gaseous cooling fluid (FIGS. 2, 3). It is likewise possible to arrange the means or cooling ducts 19 laterally. Cooling also may be implemented by means of an external cooling source.
Both the compressor 1 and the turbine 2 possess in each case an inner shell 20 (FIG. 1) which, together with the surface of the rotor shaft 4, forms a flow path 21 for the working medium and closes off said flow path outwardly. For this purpose, a plurality of heat accumulation segments 22 are releasably arranged in the axial direction between the vane bases 16 of adjacent guide vane rows 17 and 18 of the compressor 1 and of the turbine 2 and, together with the vane bases 16, form the inner shell 20 (FIGS. 1, 3).
The carrying disks 14 of adjacent guide vane rows 18 of the turbine 2 are connected in each case by means of a releasably arranged pressure ring 23 (FIGS. 1, 3). Similar pressure rings 23 are arranged in the downstream region of the compressor 1 between the carrying disks 14 of adjacent guide vane rows 17 (FIG. 1). Between each of the pressure rings 23 and the corresponding heat accumulation segments 22 is formed an annular space 24 (FIG. 3). The annular spaces 24 are connected to the compressor 1. They may, of course, also be fed with an external cooling medium from outside. The carrying disks 14 have in their inner region, in a known way, dovetail guides and the vane bases 16 correspondingly shaped counterpieces which serve for locking the compressor and turbine guide vanes 17, 18.
The outer housing 7 and the carrying disk 14 always have a largely constant temperature on account of their cooling. The vane bases 16 of the compressor and turbine guide vanes 17, 18 therefore also remain on a constant radius on the carrying disk 14. The minimum blade play can thereby be designed for the full-load point. At the same time, even in the case of a hot start, there is no risk of the brushing of the guide vanes 17, 18 against the rotor shaft 4 or of the moving blades 5, 6 against the heat accumulation segments 22. The operating play both in the case of the turbine 2 and in the case of the compressor 1 can therefore be reduced, with the result that the efficiency increases.
The vane change takes place from outside the cage-like outer housing 7 or the carrying structure, that is to say through this. For this purpose, first the pressure ring 23 is removed, and subsequently the heat accumulation segments 22 which are arranged, in the flow direction 8, upstream of the carrying disk 14 having the compressor or turbine guide vanes 17, 18 to be exchanged. A simple auxiliary device, not illustrated here, is used for supporting the vanes. Thereafter, the carrying disk 14 is displaced horizontally in its recess 15 counter to the flow direction 8. The compressor and turbine guide vanes 17, 18 are then freely accessible, so that their demounting can take place. Finally, as a result, the space for the exchange of compressor or turbine moving blades 5, 6 is also provided. Mounting takes place in reverse order.
The cruciform bearing supports 9, the longitudinal members 10 and the carrying disks 14 are preferably additionally covered with a functional layer for thermal insulation, heat protection layer 27, consisting of ceramic/mineral material (FIGS. 2, 3). Such a heat protection layer 27 is likewise arranged on the pressure rings 23 (FIG. 3). A heat protection mat may, of course, also be used. In order to ensure the stability of the connections, the respective connection regions of these components are designed without a heat protection layer 27.
However, the solution shown in FIGS. 1 to 3 entails problems which are caused, above all, by a complicated mounting/demounting of the compressor guide vanes 17 or turbine guide vanes 18 (see the abovementioned explanation relating to the vane change).
The publications U.S. Pat. Nos. 5,127,797 and 5,564,897 describe gas turbo sets, in which, in the compressor part, the guide vanes of a guide vane row are arranged in each case severally on one annular segment and can be mounted and demounted together with the annular segment. However, the fastening of the annular segments is designed in such a way that, for demounting, the entire outer housing of the compressor has to be demounted.